Cellulose acetate solution and a film formed therefrom



1 8 19, 1952 c. R. FORDYCE EI'AL- 2,607,704

7 CELLULOSE ACETATE SOLUTIQN AND A FILM FORMED THEREFROM Filed May 24,1949 FILM THICKNESS JTR/PPED F/LM THICKNESS cum-'0 (me/15$) (INCHES)23456789"/0///2/3 TIME/MINUTES) 0N CAST/N6 SURFACE/1T 70% T0807? PERCENTmm; mmmfs V PARTS OF PLASTIC/25R mwsarmayzz' apuaz'zzsmzcaaJIIjLfiENTORS BY [WW 4 ATTORNEYS Patented Aug. 19, 1952 CELLULOSEACETATE SOLUTION AND A FILM FORMED THEREFROM Charles R. Fordyce andBruce E. Gramkee, Rochester, N. Y., assignors to Eastman Kodak Company,Rochester, N. Y., a corporation of New Jersey Application May 24, 1949,Serial N0. 95,014 7 Claims. (01. 106-189) This invention relates tocellulose acetate solutions and the film base therefrom. Moreparticularly, this invention concerns improvements in cellulose acetatesolutions which permit obtaining from said solutions, at a highercoating speed, a photographic film base having overall properties atleast equivalent or superior to the film base in present large scalecommercial use and having, in addition, the valuable properties of beingrelatively noninfiammable and dimensionally stable.

This application is a continuation-in-part of our applications SerialNos. 707,807 and 707,808,,

now Patents Nos. 2,492,977 and 2,492,978. Inasmuch as our companionpatents just referred to set forth considerable detail backgroundinformation on cellulose ester solutions and film forming, only briefreference will be made herein to the problems facing the industry priorto the inventions of our patents aforementioned and the improvementinvention described in the instant specification. It appears suflicientto point out that prior to our inventions and, as established in theart, cellulose nitrate has been regarded as a standard material for themanufacture of commercial film base. Cellulose nitrate possesses theadvantages, for example, for use in commercial motion-picture film base,of high tensile-strength, flexibility, moisture resistance and rigidity.'Such properties are valuable for commercial motion-picture film since,for example, high tensile strength insures good wearing characteristicson projection and, as is well known, motion-picture film, of course, maybe projected many hundreds of times. Flexibility is essential to properbehavior on handling. Good moisture resistance and rigidity arenecessary properties for preventing dimensional change, tendency tocurl, and the like.

While, as just indicated, cellulose nitrate has in the past been thestandard material, as is also well known, cellulose nitrate film basepresents the problem and disadvantage from the standpoint of highinflammability. Therefore, it has long been recognized that it would bedesirable to have a material for motion-picture film base and similarpurposes which does not have the undesirable inflammabilitycharacteristics of cellulose nitrate but doeshave the desirablecharacteristics. Up to the time of the inventions described in ourpatents aforementioned and in the instant specification, as far as Weare aware,

no product had been developed which was successful in meeting thephysical requirements briefly outline above and which was relativelynoninfiammable as compared with cellulose nitrate film base.

There is, of course, safety film manufactured for home use and otheramateur purposes which has low inflammability and meets the conditionsfor home and amateur use for which the film is designed. Such film,which will be referred to herein as amateur film, does not possess theproperties which would render it capable of use under drastic conditionswhich are encountered in the commercial motion picture field. That is,the presently available amateur safety film, when compared withcommercial nitrate film, does not possess equivalent tensile strength,susceptibility to moisture, and like properties. In further detail, forexample, whereas the range of swell and shrink for commercial nitratefilm might be about .5% to .8 presently available partially hydrolyzedorganic ester (safety) film may show swell and shrink characteristics offrom 1.0% to 1.75

.It :is, therefore, apparent that the production of acelluloseestersolution which will give a film thatis relativelynoninfiammable but which film at the same time possesses properties ofstrength, flexibility, moisture resistance, and rigidity that are atleast of the order of the properties possessed by presently availablecommercial cellulose nitrate film is a highly-desirable result.

.We have found in accordance with the invention described in detailherein, that a cellulose acetate solution may be prepared, provided acertain type of cellulose ester is used and there is incorporated inthis solution contents of certain ingredients which, with proper castingtechnique, permit the production, at high coating speeds, of acommercialfilm base that not only possesses the. desired and comparableproperties to presently available cellulose nitrate film base, but.represents an improvement over presently available film base in itsrelative noninflammability, speed of manufacture, and in other features,as will be apparent from a consideration of the description whichfollows. i

This invention has as one object to provide cellulose acetate solutionswhich are adapted for the casting ofa relatively noninfiammable filmbase havingsuch physical properties as to render the film baseacceptable for use in the commercial motion-picture industry. Anotherobject is to provide from high acetyl cellulose acetates compositionsadapted for the casting at high speeds of commercial motion-picture filmhaving high tensile strength, good flexibility, moisture resistance,rigidity, noni'nflammability and good stability. A still further objectis to provide a susceptible of film forming over a wider range ofoperation. Another object is to provide a new uncured film base. Stillanother object is topro vide a method of manufacturing noninflammable.

film base of the class described. Another obl'ect is to provide a newfinished acetate-typefilm characterized by its dimensional stability andother improved properties. Other objects will appear hereinafter.

An understanding of the broader features of our invention will be hadfrom the general:

description which immediately follows. Thereafter will be set forthspecific examples of .our invention. In these descriptionsreference'will be made to the attached drawing forming apart of thepresent application in which Figure ,1 is a chart or graphshowingaprtain relationship between'film thickness and casting speed.Figure 2 is a chart showing relationship-with respect to the'plasticizercontent of the novelcbmpositions described in the presentapplication;

From the preceding discussions, it is apparent that cellulose nitrate(an inorganic-acid ester of cellulose) comprises the material heretoforeused commercially for film base and similar purposes but isdisadvantageous beca-use of inflammabi-lity.

The safety film compositions proposed for'fama-.

teur purposes are comprised of organicesters of cellulose, but are ofthe partially hydrolyzed acetone-soluble type.

1n contrastthereto, the cellulose ester compo nent usedin our solutionsof thepresent invention comprise a selected high acetyl 'type of organicesters of cellulose which at sometimes hereinafter may be referred to;in a general way as thetriester or tria-cetate type. gMethods' for themanufacture of the high acetyljand triester type of cellulose acetateare already' known in the art,' hence description of this aspect isunnecessary, and it will be assumed for the purposes of describingtheinstant invention that a supply of the high acetyl type of celluloseacetate .is on hand. V i

We have found that the addition of cyclohex ane'in an amount within therangeof approxi-.

mately 5% to l% to a solution of high acetyl cellulose acetate of 42.5%to 44.0% acetyl content in "methylene chloride methyl alcohol willincrease-thecoating speed in proportion to the amount added. As will be1 apparent as the description proceeds the methylene chloride compcnentmay be present in an amount of, for

example, from 65 to 90% and the methyl alcohol component in anamount inthe range of 25 to5 We have also found that for-quality of product,

greater'ithan 4% of thetotal solvent combination,

but preferably isnot incorporated in quantities greater than of thesolvent mixture because mixtures containingmore than that amount will 4not too easily dissolve very high acetyl cellulose acetate. As will beexplained, we prefer a selected acetyl within the range of 42.5% to44.0%.

In further detail, increasing amounts of cyclohexane have givenincreased rates of filmcasting, as represented by the following resultsFilm Thickness Stripping Time on When Thickness Amount of Casting inPercent Cyclohexane Surface hgreater d Mmutes Stripped Cured i z gPercent Inch Inch 5 3. 9 to 4. 0 .010 0058 4'2 8 3. 4 to 3. 5 011% .0055105 10 l "2. 8 to 3. 2 .012 .0055

In our previous applications, Serial Nos. 707,807 and 707,808, nowPatents 2,492,977 and 2,492,978, high speeds of casting were obtained byoperating under conditions outlined as area D of Figure 1 in thosepatents. Thischart reproduced as Figure l in the attached drawing,includes an area C of slightly slower casting operation speeds, whichcould not be used readily with the former solvent compositions because.of unsatisfactory stripping behavior. By use of cyclohexane in thesolvent compositions, however, we have now found that high speed castingoperations can be carried out anywhere within the areas B, C, or D andthus the usefulness in manufacturing has been greatly increased. 1 r

This is a distinct improvementnot only because of the speed advantage,but it also eliminates the area 0. The "film, when stripped, is usuallygreater than 100%"thicker than tl'le final cured thickness. Thesefigures were'obtairied using an F. casting surface. i 1

The .aspect'under consideration" ca'nj be 1 improved if the castingsurface temperature is lowered. A solution in accordance with thepresent invention for casting runs was. made in the following way:

A uniform solution of parts of cellulose acetate of 43.4% acetyl contentin 384 parts of methylene chloride and 52 parts of methyl alcohol wasprepared at room temperature. There was then added with stirring amixture'of 42 parts of cyclohexane and 42 partsof methylene chloride.After thorough-mixing there was then" Film Thickness Stripping Time onwhen- Thickness Gastmg Surface Casting in Percent Temperature Surfacegreater Mmues Stripped Cured gfiggg F Inch inch Percent The physicalproperties of support. from the cyclohexane formulae of the instantinvention are in general similar to those obtained from castingcompositions containing ethylene or propylene chloridesof ourPatents2,492,977 and 2,492,978.

This includes tensile strength, flexibility; tear strength, and Young smodulus;

There is, however, a particular improvement in swell and shrinkamplitudeby use of from about 8% to of the total solvent as cyclohexanein the formula. A- summary of this property is as follows:

Range of Swell and Shrink Amplitude (Percent) 1 Amount of CyclohexaneLength Width 7 Percent 8 57-. 65 73-. 85 56-. 65 7 2-. 87

Swell aud Shrink (Percent) Casting Surface Temperature Length Width Inthis description, it should be noted that the swell and shrink amplitudeof film support made by cyclohexane formula of the present invention isdefinitely lower than that of support made from solvent mixturescontaining propylene or ethylene dichlorides of our Patents 2,492,977and 2,492,978 aforementioned.

While we do not wish to be bound by any theory of operation, thefollowing general explanation may aid in the understanding of ourinvention. We believe that the desirably low swell and shrink amplitude,high coating speed,'and physical properties may be due to the additionof the cyclohexane to the solvent formula, which causes a coagulation ofthe cellulose triacetate type ester in the solvent mixture after theevaporation of part of the solvent. This enables the stripping of thefilm 70% to 140% thicker than the cured film thickness, after which it.-can be rapidly cured from both surfaces.

A further understanding of our invention will be had from aconsideration of the several examples which follow: In these examplesthe solutions were prepared as described above, film cas and tested togive the described data.

, Erample 1 This example illustrates a composition containing solventsin the ratio of 82% methylene chloride, 8% cyclohexane, 10% methylalcohol.

Ratio of thickness percent 105 Cellulose acetate (high acetyl) parts 100Methylene chloride do 496 Cyclohexane do 46 Methyl alcohol do 28Triphenyl phosphate do 15 Casting surface temperature F Time on castingsurface minutes 3.2 Thickness when stripped do .0122 Thickness whencured do .0057 2 Ratio of thickness percent 114 Length Width Swell andshrink, percent 65 Y [76 Tensile strength, lbs/sq. 12, 900 12, 000-Folds 12 12 Tear, grams I 45 I 52 Length Width Swell and shrink,percent. 57 I 76 Tensile strength, lbs/sq in 14, 100 12, 900 Folds V 11'9 Tear, grams 50 56 Example II This example illustrates acompositioncontaining solvents in the ratio of-f82% methylene chloride, 8%cyclohexane, 10% methyl alcohol.

Cellulose acetate (high acetyl) parts 100 Methylene chloride do 426Cyclohexane do 42 Methyl alcohol do 52 Triphenyl phosphate do 15 Castingsurface temperature F 70 v s Time on casting surface 'minutes 3.2Thickness when stripped f do .0130 Thickness when cured do .0058 Ratioof thickness percent 124 Length Width Swell and shrink, percent .60' L80Tensile strength, lbs/sq. 13, 800 11, 250 Folds .12 I -l2 Tear, grams 159 69 This example illustrates acompositio-n contain- 7 ing solvents inthe ratio of 82% methylene chloride, 8% cyclohexane, 10% methyl alcohol.

Example IV This example illustrates a composition containing solvents inthe ratio of 87% methylene chloride, 8% cyclohexane, 5% methyl alcohol.

a Example V- Thisexampl-illustrates a composition containings'olventsiii the ratio of77%' methylene chloride, 8 :cyclohexane; '15 methyl:-alcoholz'i.

Example VI This example illustrates a compositioncontainingsolventsinthe ratioof 82 "methylene -ch1o ride, 8%cyclohexane, 10%, ethylalcohoL'.

Cellulose'acetate. (high acetyl)- parts 100 Methylene chloride; do' 439Cyclohexane' do 43 Ethyl alcohol d0 54 Triphenyl phosphate; don..- 15Casting surface. temperature; .F: 75 Time On castingsurfaces. -minutesaThickness when stripped do .0130 Thicknesswhencured; do; .0056; Ratioof-thicknessipercent-; 132

-Length; Width";

Swelland shrink percenta .54? 5 .70. Tensile strengthylbsr/sq." 14,80013,000 Fol L; I 12 13 Tear,-.grams 38 43 In the above examples it willbe understood that the cellulose acetate has been used to refer toanesterh'aving a selected high acetyl range, such as containing acetylfrom 42.5 to e4..0% as already. discussed in the first partoflthespeciafication. Where casting surfacehas been- -referred to thisis intended to refer to any usual part of the instant specification andour Patents 2,492,977'and 2,492,978.

ln -thefirs't part of this specification, We pointed out that theretention of-cyclohexane becomesless as the plasticizer content of thecoating composition is increased. The amount of plasticizer' of ourcomposition has been varied from 5% to 25% in-runsdesigned for'fihnsupport. In addition, suchformulas have :also been used to coat anacetate sheeting support (wrapping sheeting) for this latter productplasticizer.

In "the case-of. the iihnruns, triphcnyl phosphat e'has been used. Thegraph of Fig.2 shows" the advantage of increased amountsof plasticizer.

The products-represented in-this Fig,- 2 curve concerning residualsolvent content :were-prepared by use of aboutmaximumcuring-teiiiperatures which appear practical for commercial use:This is because higher temperaturesresult in excessive loss ofplasticizer from =the-co1np0sition during the curing operation.The-curve thus represents approximately the lowest practical residualsolvent content for each-'plastioizer content.

It is desirable to maintain a comparatively low levelof residual solventin photographic film support, because if allowed to remain inthe film,it may slowly volatilize during aging, causing a correspondingdimensional shrinkage of the product. Investigation has shown that theresidual solvent preferably should not be greater than". 6% to 8% forbest shrinkage quality. Itis, there-.- fore, a feature of the preferredembodiment of our composition that it contain a plasticizer or mixtureof plasticizers in amount-of at least 10 parts for 100 parts ofcelluloseacetat r On the other hand, however, excessiveamountsl' 0fplastic'izer also :are somewhat unsatisfactory because of loss ofstrength in the film support.- For this reason the amount-of plasticizerin' our preferred embodiments is not greater than-about 30 parts for 100parts of-cellulose acetate In the range fromlito 20% pla'sticizer itwill be observed that the slope of the-curve-of-Fig.=2 is' quitelinearshowing almost an' even'exchange I of solvent for plasticizer.

The following table summarizes the'physicalproperties of aeelluloseacetate (high acetyl) dissolved in a solventcomposition of 32methylene chloride, 8% cycloh'exane, 10% methyl al cohol with varyingplasticiz'er' content:

Wehave used. 30% of.

Parts Cellulose acetate (high acetyl) 100 Methylene chloride 426..Cyolnhpzane 42 Methyl alcohol; 52

(Parts per 100 parts of acetate):

Plasticizer Oontent,'Percent 5 l0 15 20 25" Time on casting surface,minutes 3:4 3. 4 3. 4 3. 3. 4 Thickness when stripped 0110 0110 01150118 0118 Thickness when cured 0057 .0058 0057 0056 0057 Swell andshrink, percent:

Length .10' .53 .57.; .601: .56 W .82 .73.. .84 H ,73 .67

s 10" 10 l 11) i 11 9 1.3- 11 1 12 I 9 1 casting surface sucha$---are-usedin-proeesses-offilm forming, such as.whee1s,.continuousxbands orgother .similar film formingapparatusr The":

other items appearingflinqtheexamples .will -be:

apparent atothose skilled in the art, particularly It will be noted thatthe tensile strength ofith'ei products containing ,5and:10%;;plastioizer: are": inferior to those of,higher.:plasticizercontent; This is because of the comparatively?largeramount of residual .solvent. remaining in those in the light of thegeneral description in the first 7 films. Higher plasticizer ratiosafford more efiieient curing of- 1. t e

films, with consequently higher strengths? In the aboVe'fiesciiptiQntriphenyl phosphate k has been referred to as theplasticizer; i This type 'otplasticizer is preferred because-of itsnon-c inflammable nature. However, other plasticizers suitable for-filmuse such as tricresyl phosphate, diethyl phthalate, -dibutyl phthalateand tripropionin may be used either alone in place of or in conjunctionwith thetriphenyl phosphate The graphic representation of. Fig. 1 has ialready been briefly discussed. above r-for showing that inaccordancewith the-present invention high stripping speeds may be accomplished notonlyin areas B and D but also in area 9. This, of course; permits awider-range of operation.

In our'companion patents the significance of the other referencecharactersy-A, E, etc., are set forth. However, for the purpose ofcompleteof improved operation which is faster than operations under A;area B, for example, representing operations in accordance with ourcompanion patents already referred to above.

The area C represents a range of operations which, while faster thanthose falling under area B, could not be used readily with castingcompositions described in our Patents 2,492,977 and 2,492,978 becausethey resulted in a residual deposit on the casting surface. In thepresent application, however, the use of cyclohexane has eliminated thiscondition and permits entirely satisfactory casting operation anywherewithin the areas B, C, or D. It may be seen from the foregoing that arearepresents an operative area and that B and D also comprise usefulareas. Accordingly, it is apparent that an extension of the boundariesof area C may also be considered as constituting the boundaries of areasB and D.

Line E represents an approximate boundary with respect to which thestripping character of the film tends to become somewhat unsatisfactoryas the conditions of operation are brought outside of area D and into anarea beyond line E.

It is believed that from the foregoing it will be seen that we haveprovided improved cellulose acetate solutions for film forming overextended areas of operation, methods of making said solutions andconverting the solutions to partially and finally cured film base ofcommercial value. With respect to this latter item, it is believed thatwe have produced, as a new product, dimensionally stable acetate filmcapable of being easily spliced, which contains as an essentialcomponent acetate with selected high acetyl. By employing a selectedhigh acetyl, preferably within the range of from 42.5% to 44.0%, readysolution is obtained. On the other hand, if a triacetate say of 44.8%acetyl is employed there may be some difficulty from the commercialstandpoint of getting this into solution satisfactorily and rapidly. Inaddition, by employing the selected high acetyl range we have set fortha finished cured film which may be more easily spliced as compared witha completely esterified (triacetate) film is obtained.

comparedfor' example with average amateur film m whichmaly showswelland-shrinkcharacteristics of from 1 .0% to 1.75% As poin tedoutfi ournew i film'is relatively-noninflammablei 0th tages will be apparent'tothoseskilled' What we claim is: i 1. A cellulose acetate solutioncapable of being rapidly formed into a relatively noninfiammable filmbase comprised essentially of cellulose acetate having an acetyl contentbetween 42.5 and 44% capable of being rapidly'formed into a relativelynoninfiammable nonbrittle film base, the solution consisting essentiallyof cellulose acetate having an acetyl content between 42.5% and 44%,this cellulose acetate being dissolved in a solvent essentiallycomprised of methylene chloride 65 to 90%, methyl alcohol 25 to 5% andcyclohexane greater than 4% and not greater than 10%.

3. A cellulose acetate film-forming solution capable of being rapidlyformed into a relatively noninfiammable nonbrittle film base, thesolution consisting essentially of cellulose acetate having an acetylcontent between 42.5% and 44%, this cellulose acetate being dissolved ina solvent essentially comprised of methylene chloride 65 to 90%, methylalcohol 25 to 5% and cyclohexane between 8 and 10%.

4. As a composition of matter a cellulose acetate film-forming solutioncapable of being rapidly formed into a relatively noninfiammablenonbrittle film base, said solution being composed of cellulose acetatehaving an acetyl content within the range of 42.5% to 44% dissolved in asolvent mixture consisting essentially of methylene chloride, andunsubstituted aliphatic monohydric alcohol of 1 to 2 carbon atoms andcyclohexane in amount greater than 4% but not greater than 10%.

5. As a composition of matter a cellulose acetate film-forming solutioncapable of being cast into a relatively noninfiammable nonbrittle filmbase, this solution consisting essentially of cellulose acetate havingan acetyl content between 42.5 and 44%, the cellulose acetate beingdissolved in a solvent composed of methylene chloride and unsubstitutedaliphatic monohydric Length Width Swell and shrink, percent not greaterthan about 0.6 0.8 Tensile strength, lbs./sq. in. not less than about12, 900 11, 250 Folds not less than about 12 12 Tear, grams not lessthan about .l 38 43 7:11 17; A relativelymoninflammable; ilonbrittle,dimensionally; stable; finished; acetate film capable ofbeingreadilysspliced aandpharacterizedain that it 'is composed.substantially,entirelyv of-plasti'cized cellulose EacetateW-hereinthe'fcellulose acetate has an acetyli contentrbetween:;42;5.% and 447%;-and

- the finishedifilm having; properties of the following order:

'vIJeiig'the V'Width swellznand shrink; percent not gr'eaiteritheuabout.. .o; 0.8

TQILS yab t 11,250 12 43 seid film'fhati'rigioeen deposited from acomposiaemteiwoizs cimn The following 'rfei'en'cesgare io fireeordziin"the *fileiof thispatent N T D 'STAPTE$ PKIiENT 'f

1. A CELLULOSE ACETATE SOLUTION CAPABLE OF BEING RAPIDLY FORMED INTO ARELATIVELY NONINFLAMMABLE FILM BASE COMPRISED ESSENTIALLY OF CELLULOSEACETATE HAVING AN ACETYL CONTENT BETWEEN 42.5% AND 44% SAID CELLULOSEACETATE BEING DISSOLVED IN A SOLVENT COMPOSED OF METHYLENE CHLORIDE 65TO 90% METHYL ALCOHOL 25 TO 5% AND CYCLOHEXANE 5 TO 10%